Process for the production of diolefins



Patented Apr. 27, 1948 UNITED STATE s PATE NT OFFICE PROCESS FOR THE PRODUCTION OF I OLEFINS' Wilson D. Seyfried, Wooster, and Sam H. Hastings, Baytown, Tex., assignors to Standard Oil Development Company, a corporation of Delaware Application June 13, 1944, Serial No. 540,078

2 Claims. (Cl. 260-680) .rected to the production of a diolefin including the step of subjecting a mixture of mono-oleflns to dehydrogenation conditions.

At the present time. there is an active com; mercial demand for diolefins and particularly for the C4 conjugated diolefin, butadiene-1,3. A conventional process for producing butadiene is by the passage of butylene through a dehydrogenation zone to convert the C4 mono-olefin into the C4 diolefin. Whencarrying out this operation, the amount of butadiene obtained as a product is a function of the quantity of butylene feed stock and under the present economic conditions the demand for butadiene substantially exceeds the amount of butylene available as feed stock.

It is, therefore, an object of the present invention to produce increased amounts of a desired 'diolefin by charging to a dehydrogenation zone major portion of diolefins obtained from dehy- This is an unexpected discovery because heretofore in the art it has been accepted that the most efiicient operation for producing a given diolefin by dehydrogenation involved the feeding of a substantially pure mono-olefin, having the same number of carbon atoms as the desired diolefin, to the reaction zone and if other mono-oleflns were present in thereaction zone they would act as a diluent and decrease the efiiciency of the reaction. It was accordingly surprising to find that a feed including substantial amounts of mono-olefins having one more carbon atom than the desired diolefin in admixture with substantia l' amounts of mono-olefin having the same number of carbon atoms as the desired diolefins gives, on dehydrogenation, substantially the same percentage yield of diolefin as a feed consisting of the mono-olefin having the same number of carbon atoms as the desired diolefin. As a spe- "ciflc example, we have discoveredthat a mixture .the mono-olefins separately, such as butylenes drogenation of. butylene was butadiene-1,3 and the major portion of dioleflns obtained from dehydrogenating pentylene were conjugated pentadienes. When practicing the present invention, the yield of diolefin, such as butadiene, is clearly in excess ofthat which would be obtained by separately dehydrogenating substantially pure mono-olefins, such as butylenes and pentylenes.

The dehydrogenation of the mixture of monooleflns to produce diolefins in accordance with the present invention may be conducted inaccordance with the principles well known to the dehydrogenation reaction. It is preferred to conduct the dehydrogenation reaction at temperatures in the range of 1150 to 1300 F. and with pressures ranging from 1 to 2 atmospheres absolute. The catalyst employed may be any well known dehydrogenation catalyst and the hydrocarbon mixture is preferably mixed with from 3 to 15 volumes of superheated steam per volume of hydrocarbon and passed over the catalyst at space velocities ranging from 200 to 500 volumes of feed per volume of catalyst per hour.

An embodiment, suitable for the practice of the present invention wilLnow be described in conjunction with the drawing in which the sole figure is in the form of a diagrammatic flow sheet.

Turning now specifically to the drawing, a pentylene fraction is charged to inlet II and a recycle pentylene fraction passed through line l2 and the two fractions mixed together in line l3 and passed into storage vessel l4. A butylene fraction is charged to the system through inlet I5 and a recycle butylene fraction passed through recycle line I6 and the two components mixed together in line H and passed into butylene storage vessel l8.

Pentylene is withdrawn from storage vessel I4 0 through line l9, and butylene is withdrawn from storage vessel l8 through line 20 and the two streams are mixed together in line 2|. It is to be emphasized that an essential feature of the present invention is the use of a feed containing a mixture of mono-olefins and usually it will be desirable for the stream in line 2| to consist of approximately 50 per cent butylenes and 50 per cent pentylenes. This mixture is heated to a temperature in the range of l to l3(l0 F. by

being passed from line 2| to'furnace 22 and the heated mixture from furnace 22 is withdrawn through line 23 into line 24 at which point substantial amounts of hot steam are added thereto through inlet 25. The quantity of steam employed may be varied from 3 to 15 volumes of steam per volume of hydrocarbon feed and should be heated to approximately the same temperature as the hydrocarbon by being passed through furnace 26. The mixture of hydrocarand pentylenes, and in this known process the 0 bons and steam in line 24 is passed into dehydrogenation reactor 21 containing a suitable dehydrogenation catalyst and maintained at the temperature of 1150 to 1300 F. to convert substantial amounts of the mono-olefin feed into butadiene. i

Following the dehydrogenation step, the reaction products and the steam from the reaction zone are reduced in temperature as rapidly as possible by the introduction of a water spray into the lower portion of the dehydrogenation'reaction zone by means of line 28, and by a heat exchanger 29, an oil quenching zone 39 and a water quenching zone 3|. The mixture of hydrocarbon reaction products and steam is withdrawn from dehydrogenation zone 27 by line 32 and passed through heat exchanger 29, which is in the form of a waste heat boiler, and thence by line 33 into oil quenching tower 30. The vapors pass from the oil quenching zone through line 34, containing cooler 34', and into separator 35 to separate water from the hydrocarbon vapors and from this operating zone the vapors pass on through 36 to water quenching tower 3 I. Vapors from water quenching tower 3| are withdrawn through line 31, passing into a second settling drum 38 to remove condensate through line 38' from the vapors, and thence through line 39 containing compressor 40 and cooler 4|, into separating vessel 42.

The liquid accumulating in vessel 42 contains the desired butadiene. Accordingly, this fraction is withdrawn through line 43 containing pump 44 and cooler 45 and discharged into a distillation zone 46 where it is separated into a light fraction withdrawn as overhead through line 41, a C4 fraction withdrawn as a side stream through line 48,3. C fraction withdrawn as a side stream through line 49 and a heavier fraction withdrawn as bottoms through line 50. It is to be understood that although a single vessel is shown for conducting this distillation step, in practice it may be desirable to employ a series of distillation columns. The C4 fraction is passed through line 48 to a butadiene extraction plant 5| and from this plant a finished butadiene fraction is discharged through outlet 52 and butylenes for recycle to the dehydrogenation step via line- [6.

the oil flowing in line 59 by means of connection 62 containing cooler 62' to form a mixture used as quenching oil in tower 30 and the remainder flowing through branch 63 to stripping tower 64. In this stripping tower the lighter constituents are removed as vapor and returned to the quench ing tower through line 10, and the lean oil is re.- moved via line 51 containing pump 65 and passed into absorber tower 55. If desired, make-up lean oil may be added to the oil being circulated through line 59 via inlet 66. Water quenching tower 3| is conventional and is provided with water circulating line 61 containing pump 68 an cooler 69.

Water is introduced through line H into waste heater boiler 29, picks up heat from the hydrocarbon reaction products introduced by line 32, and is converted to steam. This steam discharges from waste heater boiler 29 by line 12, admixes with steam introduced into the system by line 25, passes through furnace 26. and then intermingles with the mixture of pentylene and butylene in line 24 as described.

The following specific examples are givenfft illustrate the advantages of the present invention. It will be seen that in Example 1 the monoolefin in the feed was butylenes, in Example 2 the mono-olefin in the feed was pentylene, while in Example '3 the feed contained a mixture of equal amounts of butylene and pentylene. In each example the dehydrogenation catalyst used was identical and consisted of approximately 80 per cent MgO, 14 per cent F8203, 3 per cent K20 and 3 per-cent CuO. In each example also the hydrocarbon feed was admixed with steam in the ratio of 1 part of hydrocarbon to 9'parts of steam and the diluted feed was then passed over the catalyst at the rate of 500 volumes of feed per volume of catalyst per hour.

Example 1 The hydrocarbon feed stock containig 60 mole per cent of normal butylenes and 40 mole per cent of substantially non-reactive butanes'was passed over a catalytic mass with an inlet tempererature of 1200 R, an outlet temperature of 1150 F. and an average catalyst temperature of The C5 hydrocarbons are discharged through line 49 to pentadiene extraction plant 53 and a finished pentadiene fraction is withdrawn through outlet 54 and pentylenes are withdrawn through line 12 for recycle to the dehydrogenation unit. Butadiene extraction plant 5| and pentadiene extraction plant 53 may both employ as a solvent an ammoniacal cuprous acetate solution. Any solvent may be employed which will form addition products with the diolefins and which will release the diolefins on suitable treatment.

It is prefered to operate oil quenching tower 30 in conjunction with an absorber unit 55. -In vessel 42, the uncondensed fraction may contain appreciable amounts of desirable C4 and C5 hydrocarbons. These vapors may be passed through line 56 to absorber vessel 55 where they flow countercurrent to a stream of oil injected into an upper portion of vessel 55 via line 51. The unabsorbed vapors from absorber vessel 55 may be removed from the system via outlet 58. Rich absorber oil is withdrawn from the bottom of absorber 55 by means of line 59 and may be returned to the top of quenching tower 39 to act as quenching oil therein. The oil accumulating in the lower portion of oil quenching tower 30 is removed through line 60 containing pump BI and the stream split, with a portion being'added to 1175" F. The product removed from the outlet was rapidly quenched- Upon analysis it was found that the conversion of butylenes was 30 per cent and the yield, of butadiene 22.5 per cent.

Example 2 A feed stock containing 60 mole per cent of pentylenes and 40 mole per cent of substantially nonreactive pentanes was passed over the catalytic mass used in the preceding example with an inlet temperature. of 1200 F. and an outlet temperature of 1180 F. and an average catalyst temperature of 1190 F. The product removed from the outlet was rapidly quenched. Upon analysis it was found that 30 per cent of the' pentylenes had been converted and the yield of :butadiene was 15 per cent.

Example 3 A feed stock containing 30 mole per cent of normal butylene, 30 mole per cent of pentylene and 40 mole per cent of substantially non-reactive butanes and pentanes was passed over the same catalyst employed in Examples 1 and 2. The inlet temperature to the reactor was 1200 F., the reactor outlet temperature was 1165- F. and the average catalyst temperature was 1182 F. The product obtained was rapidly quenched.

,a carbon to carbon linkage.

Upon analysis it was found that 41 per cent of the butylenes had been converted, 40 per cent of the pentylenes had been converted and the yield of butadiene was 22.9 per cent of the feed.

It will be seen that the feed stock containing equal amounts of butylene and pentylene used in Example 3 gave approximately the same yieldas the feed stock containing butylene in Example 1. In contrast, the feed stock containing pentylene used in Example 2 gave a substantially lower yield of butadiene than did either of the feed stocks of Examples 1 and 3. It may be stated that appreciable amounts of pentadienes were obtained in the product of Example 2 but, as before explained, the commercial demand at the present time is for the C4 diolefins rather than for the C5 diolefins and the amount of the C5 dioleflns present in the product was not determined. The reason for the unexpected'high yields of butadiene when using a mixture of butylene and pentylene is not known but the fol-,

lowing hypothesis is presented as a possible explanation.

When hydrocarbons are subjected to pyrolytic decomposition, approximately 67.000 B. t. u. per pound mole are consumed in breaking carbon to hydrogen linkage while approximately 20,000 3. t. u. per pound mole are consumed in breaking If a butylene feed stock is passed over a dehydrogenation catalyst in the presence of steam to form butadiene, the large quantities of heat required i or breaking the carbon to hydrogen linkage results in a substantial temperature drop across the reaction zone. Since, for catalyst of the same activity (other operating conditions being the same), substantially higher yields of butadiene are obtained at higher average catalyst temperature, it would seem that improved yields would be obtained by maintaining higher average catalyst temperatures for a given inlet catalyst temperature. By introducing along with the C4 mono-olefin, a substantial portion of C5 mono-olefin in accordancewith the present invention, the C5 fractions are subjected to a combination of cracking and dehydrogenation. The smaller amount of heat required for breaking the carbon to carbon linkage in cracking the C5 hydrocarbons in comparison to the heat required for dehydrogenation, produces a higher average catalyst temperature in the reaction zone. These higher average catalyst temperatures are clearly indicated in the examples in that the temperature drop across the catalyst bed in Example 3 is only 35 F. compared to the temperature drop of 50 F. in Example 1.

While we have given specific examples illustrating the practice of the present invention, it will be understood that they are given by way of illustration and not by way of limitation. While it is preferred to employ a feed containing approximately equal amounts of butylene and pentylene as the feed for the dehydrogenation zone for producing butadiene, the invention is not restricted to a feed of these proportions. It has been found that the composition of the feed may range from 3 parts of butylene and 1 part of pentylene to 1 part of butylene and 3 parts of pentylene and good results will be obtained although the preferred range of proportions is from 40 per cent butylene and 60 per cent .pen-

tylene to 60 per cent of butylene and 40 per cent pentylene. It is also to be understood that the invention is not limited to the production of C4 dioleiins but may be employed for producing other diolefins, such as C5 and Cs diolefins. In its essence, the inventive feature resides in using, as a feed to a dehydrogenation zone for the production of a given diolefin, a mono-olefin having the same number of carbon atoms as the desired diolefin, in admixture with a mono-olefin having one more carbon atom than the desired diolefin. I

Having fully described and illustrated the practice of the present invention, what we desire to claim is:

1. In the production of butadiene, the steps comprising forming a hydrocarbon mixture including butylene and pentylene in the ratio of about 3 parts of pentylene per part of butylene to about 3 parts of butylene per part of pentylene, feeding said mixture and superheated steam into a dehydrogenation zone containing a catalyst comprising about per cent MgO, 14 percent Fezos, 3 per cent K20, and 3 per cent CuO and maintaining said mixture and steam in said zone at a temperature in the range of about 1150 F. to about 1300" F. for a time sufficient to convert substantial amounts of said mixture to butadiene whereby a substantially greater yield of butadiene is produced than is producible under comparable conditions from said butylene alone.

2. In the production of a desired conjugated diolefin containing from 4 to 6 carbon atoms to the molecule, the steps which comprise forming a hydrocarbon mixture including a first monoolefin having the same number of carbon atoms as the desired diolefin and a second mono-olefin having one more carbon atom than said diolefln and capable of undergoing a splitting reaction to form said diolefin, said mixture includingsaid mono-olefins in the ratio range of about 3 parts of said first mono-olefin per part of said second mono-olefin to about 3 parts of said second monoolefin per part of said first mono-olefin, feeding said mixture and superheated steam into a dehydrogenation zone containing a catalyst comprising about 80 per cent MgO, 14 per cent FezOs, 3 per cent K20 and 3 per cent CuO, and maintaining said mixture and steam in said dehydrogenation zone at a temperature in the range of about 1150 F. to about 1300 F. for a time suificient to convert substantial amounts of said mixture to said desired diolefin whereby a substantially greater yield of the desired diolefin is produced than is producible under comparable conditions from said first mono-olefin alone.

WILSON D. SEYFRIED. SAM H. HASTINGS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

